What netmeg said.
Affiliate marketing is one of those things Google never was very good at. Why keep investing in something you're just not great at when there are things you've totally cornered the market in?
Does this mean they're getting ready to drop the ax on affiliates - again? I don't see why - they've been hammered enough. Affiliate links are not a sign of poor quality in and of themselves. It's just when the site has no value to the searcher that they become an issue. I think maybe Google has better ways of recognizing value in sites than looking for affiliate links.
One thing I have noticed lately, however, is a lot of websites becoming more transparent about affiliate links, placing buttons or text to let readers know a page contains them. The FTC requires transparency, so Google could possibly feel pressured to rank affiliate sites higher if they are in compliance. Also, Matt Cutts has said repeatedly to put nofollow on any link you might make money on, even though Google is pretty good at sorting that out itself. I personally think it's worth the extra two seconds to slap it on there.